1. Field of the Invention
Hydraulically driven injection pumps via injectors to be operated hydraulically execute a control event, which brings about the end of supply and the applicable onset of supply, by means of a movable control element. The control element is triggered within very short switching times, which can be less than 2 ms. The strokes that the control element executes are longer than 0.3 mm.
2. Prior Art
In injectors that communicate with a high-pressure collection chamber (common rail) that is common to a plurality of injectors, or in hydraulically driven injection pumps, very short switching and trigger times may be necessary for executing stroke motions of a control element. The requisite switching times can be less than 2 ms; in very small units acted upon hydraulically, that is, units with a very small flow cross section, direct magnet control can be employed where a 3/2-way control element can for instance be embodied, if stroke motions that are shorter than 0.3 mm in stroke length are to be executed by the control element. If longer control element strokes are needed, then direct magnet triggering of the control element, embodied as a control slide, runs up against its intrinsic limits.
Another variant is servo-triggering of the control slide, but it can be achieved only whenever the stroke lengths to be traversed by the control element to close the control edges do not exceed the aforementioned limits.
Once again, the same restriction applies, that the servo-triggering can be used preferably only in small units of small flow cross section, in which the adjusting forces are accordingly still within the order of magnitude that can be handled with servomotors. In use in large diesel engines, which require adjusting units with a relatively large flow cross section, conversely, both greater flow quantities and as a result greater adjusting forces occur, which cannot be controlled using servomotors alone or by triggering the control slide only magnetically.
With the embodiment of the invention, direct electronic regulation of a valve unit for relatively large flow cross sections is now feasible, which is also suited, among other applications, to large diesel engines. Because of the high pressures that then occur, high adjusting forces arise, which can be controlled with the proposed embodiment that is reinforced with a force reservoir. The longer adjusting paths with larger units can be traversed substantially faster with the embodiment according to the invention, and the incident closing forces can be furnished more quickly; the degree of overlap of the control edges between the control element and the surrounding housing can be selected such that effective sealing off of the high-pressure line from the pressureless outflow line is attainable.
The system reliability if the supply voltage fails is assured by the subjection of the inlet-side end of the control element to a force reservoir that reinforces the closing motion of the control element. The force reservoirxe2x80x94embodied for instance as a helical springxe2x80x94associated with the inlet-side end is dimensioned such that in the event of a voltage failure at one of the actuating devices, closure of the high-pressure inlet line is always assured. To limit the opening and closing of the high-pressure line and the pressureless outlet, stops that limit the prestressing of the force reservoir are provided in the housing bore that surrounds the control element.
The control element of the inventionxe2x80x94embodied as a control slidexe2x80x94can for instance communicate with an injection nozzle, in order to inject fuel, which is under extremely high pressure, into a combustion chamber, or can serve to supply a hydraulically operatable piston pump. With the embodiment of the control element as a force reservoirxe2x80x94reinforced control system, according to the invention, the briefest possible switching times can be achieved, yet the stroke paths are still lengthened. The short switching times at the control element are feasible because one force reservoir each, assigned to the end of the control element, reinforces the control element motion executed by the triggering of one of the actuating devices and thus shortens the switching time. Depending on the dimensioning of the spring, preferably embodied as helical springsxe2x80x94connected either in parallel or in seriesxe2x80x94the system reliability in the event of a current failure can be achieved by providing that in a current failure, the force reservoir that reinforces the closing of the high-pressure inlet line is dimensioned larger, in order to generate higher closing forces on the inlet-side end of the control element embodied as a control slide.